From owner-freebsd-bugs  Sat Mar 23 21:26:44 2002
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Date: Sat, 23 Mar 2002 21:25:50 -0800
From: Terry Lambert <tlambert2@mindspring.com>
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To: Willie Viljoen <will@laserfence.net>
Cc: freebsd-fs@freebsd.org, freebsd-bugs@freebsd.org
Subject: Re: Soft update instability with heavy IO and offboard IDE controller
References: <20020323205001.R204-100000@phoenix.vh.laserfence.net>
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Willie Viljoen wrote:
> Although no system settings seem to exist to disable write caching from
> the BIOS of my motherboard or my controller, I tried to do this with the
> hw.ata.wc sysctl as described in the handbook (I know I should have
> checked there fist)
> 
> To my dismay, this sysctl claims to be read-only on my system, and I'm
> still stuck with write caching enable. Could this lock be caused by the
> driver for my ATA-100 controller, or do I need to add some kernel options?

This parameter has to be set at boot time, either in the loader.conf
file, or by hand by interrupting the load and setting it in the boot
environment before continuing to boot the kernel.

If you are using an IDE RAID controller, this may have to be set
by talking to the controller, since the drives are not directly
under your control.  If it is merely a RAID controller that
appears to be an ATA drive, it should propagate through, no
problem, if the controller is correctly designed.

-- Terry

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